Field of the Invention
The present invention relates to a torque modification apparatus for use with a door closer and more particularly to a torque modification apparatus which varies the torque applied to a door by a door closer to ensure that sufficient torque is provided on the door to effect latching thereof when the door approaches its closed position.
Door closer assemblies are well known in the art. In known door closer assemblies the door is connected to an operating shaft of the door closer by a closer arm. When the door is manually opened the closer arm is rotated to rotate the operating shaft of the door closer. The operating shaft of the door closer is connected to a device to convert rotary motion to linear motion, typically a rack and pinion assembly which is spring biased to bias the door to a closed position. When the door is manually opened the operating shaft of the closer is rotated and the rack and pinion assembly act to compress the door closer spring. The manual compression of the door closer spring provides the closing force to enable the door to close. When the door is released, the compressed spring establishes its biasing force on the rack and pinion assembly which is transferred to the door via the operating shaft and the closer arm to close the door.
The force established by the compressed spring of the prior art door operators is nonlinear. When the door is fully opened the door closer spring, which generally is a helical spring, is fully compressed and the force exerted by the closer spring on the door will be maximized. As the spring expands and effects closing of the door the forces exerted by the door closer spring decrease. Thus, a normal prior art door closer is adapted to exert maximum closing force on the door when the door is in its fully opened position and exerts a decreasing force on the door when the door approaches its fully closed latched condition and the closer spring is expanded. In some known closers multiple lever arms are utilized to increase the torque applied to the door but such lever arm systems such as a four bar linkage do not conveniently fit in compact spaces such as behind a door. In confined spaces such as behind a door a track is used to connect the closer arm to the door and such track systems do not increase the torque applied to the door by the operator.
It is advantageous to increase the closing torque on the door when the door approaches its fully closed latched position. As the door is latched in its closed position, the door must overcome the mechanical forces associated with the latch to effect latching of the door in the closed position. Many known door closers, however, decrease the torque exerted on the door as the door approaches its latched condition. In some cases, the closer does not provide sufficient latching torque on the door to enable the door to overcome the forces of the mechanical latch and positively move to its fully closed latched position. This is especially a problem in buildings which maintain a positive air pressure therein as compared to the outside air pressure. In such pressurized buildings additional latching force is required to overcome the air pressure acting on the door.
Many modern buildings require fire walls and fire doors. These doors are equipped with hardware to assure closing and latching of the doors in the event of a fire to prevent the spread of fire and smoke. In such a fire condition, it is extremely important that the door closer produce sufficient force to latch the fire door during a fire condition. In the known prior art, in order to produce sufficient force to insure latching of the fire door at its closed position a larger door operating spring was utilized in the door closer. However, many fire doors are utilized with hold open devices which hold the door open against the force of the door closer spring until the electrical energy which energizes the hold open device is interrupted to deenergize the hold open device and release the door. If an inordinately large closer spring is utilized, the known hold open devices will not be strong enough to hold the door in its open condition against the biasing force of the closer spring.
Thus, the present invention provides a new and improved torque modification device for use with a door closer which is adaptable to modify the torque exerted by the door closer on the door without the use of a four-bar linkage to insure sufficient torque when the door approaches its fully closed latched position to overcome any forces associated with the mechanical latch and wherein the torque applied to the door when the door is in its held open position is not sufficient to overcome the holding force of known prior art door holders.